(a) Field of the Invention
The present invention relates to a switch control circuit, a power factor corrector, and a driving method thereof.
(b) Description of the Related Art
An ampere total harmony distortion (referred to as “ATHD”.) may be generated when a high voltage is input to a power factor corrector.
For example, a conventional single stage power factor corrector is realized by a flyback converter, and is operated with a critical conduction mode. In the single stage power factor corrector, an input current may be distorted by a primary reflection voltage.
A waveform of the input current according to the critical conduction mode is influenced by a duty of the flyback converter, and the duty is determined by an input voltage ratio (VIN/VR) between the input voltage VIN and the primary reflected voltage (VR). The primary reflected voltage (VR) is a voltage of which a turn ratio n is multiplied by a sum of an output voltage of the flyback converter and a voltage of both terminals of a secondary rectification diode. In detail, Equation 1 represents the duty (d) in the critical conduction mode.
                    d        =                  1                                    1              +                                                                    V                    ln                    Peak                                                        V                    R                                                  ·                                      |                          sin              ⁡                              (                Θ                )                                      |                                              (                  Equation          ⁢                                          ⁢          1                )            
Here, the input voltage VIN is a voltage on which an AC input is full-rectified such that it is dependant on a sine wave, and the input voltage VIN is dependant on a value VInPeek·|sin(Θ)| of which a sine function sin(Θ) is multiplied by a peak (VInPeek) of the input voltage. In Equation 1,
                    V        ln        Peak                    V        R              ·    |      sin    ⁡          (      Θ      )        |represents an input voltage ratio.
Also, the input current is represented by Equation 2.
                                                                                          I                  ln                                ⁡                                  (                  θ                  )                                            =                                                                    1                    2                                    ·                                      I                                          Q                      ⁢                                                                                          ⁢                      1                                        MaxPeak                                    ·                                |                                  sin                  ⁡                                      (                    Θ                    )                                                  |                                  ·                  d                                                                                                        =                                                I                                      Q                    ⁢                                                                                  ⁢                    1                                    MaxPeak                                ·                                                      |                                          sin                      ⁡                                              (                        Θ                        )                                                              |                                                        2                    ·                                          (                                                                        1                          +                                                                                    V                              ln                              Peak                                                                                      V                              R                                                                                                      ⁢                                                 |                                                  sin                          ⁡                                                      (                            Θ                            )                                                                          |                                            )                                                                                                                              (                  Equation          ⁢                                          ⁢          2                )            
Herein, IQ1MaxPeek means a peak of the current flowing to a power switch of the flyback converter.
As described above, the input current receives the input voltage ratio such that it may be distorted, and may not be dependant on the sine wave.
FIG. 1 is a waveform diagram showing an input current of a conventional stage power factor corrector according to an input voltage ratio.
As shown in FIG. 1, as the input voltage ratio is increased, the waveform of the input current is not dependant on the sine wave. In detail, as the input voltage ratio is increased, a deformation degree of which the input current is increased near a zero current and then is flat in a peak region is increased. Thus, a difference for the waveform of the input voltage is increased.
FIG. 2 is a waveform diagram showing a waveform of an input current along with an input voltage when an input voltage is 265Vac.
As shown in FIG. 2, compared with the waveform of the input voltage, that is, the sine wave, the input current has a steep slope near the zero currents A1 and A2 and a shallow slope near a peak current B.
This difference between the waveform of the input current and the sine wave causes the ampere total harmony distortion. It is preferable that the ampere total harmony distortion of the power factor corrector is small.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.